Loans and the Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Financing Receivable, Recorded Investment [Line Items]
Net deferred loan fee income (costs)	$ 13,600,000		$ 13,600,000		$ 11,900,000
Un-accreted discount on purchased loans from acquisitions	328,100,000		328,100,000		10,500,000
Provision for credit losses on loans and loan commitments			72,069,000	$ 14,581,000
Reserve on accrued interest related to CARES Act	$ 100,000		$ 100,000
Percentage of national unemployment projection	4.60%		4.60%
Expected average percentage of national unemployment in future	5.20%		5.20%
Accrued interest receivable for loans	$ 87,900,000		$ 87,900,000		62,200,000
Accrued interest receivable for loans related to CARES Act	13,800,000		13,800,000		13,900,000
Aggregate amount of residential real estate, home equity and consumer loans classified as substandard	47,000,000		47,000,000		23,300,000
Internally assigned loan grades to residential real estate, home equity and consumer loans	9,900,000		9,900,000		4,500,000
Unfunded commercial loan commitments	34,800,000		34,800,000		36,100,000
Modifications loans	4,174,000	$ 5,275,000	52,064,000	27,209,000
TDRs defaulted	312,000	211,000	3,786,000	346,000
Other real estate owned	662,000		662,000		649,000
Net charge-offs			7,100,000	8,157,000
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Provision for credit losses on loans and loan commitments			9,539,000	1,320,000
Modifications loans	2,156,000	164,000	2,642,000	739,000
TDRs defaulted	123,000		123,000	118,000
Other real estate owned	700,000		700,000
Foreclosure proceedings in process on residential real estate loans	11,300,000		11,300,000		$ 4,000,000
Net charge-offs			213,000	157,000
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Modification to allowance due to modified loan subsequently defaulting	0		0
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Provision for credit losses on loans and loan commitments			16,833,000	9,297,000
Modifications loans	$ 1,153,000	505,000	6,066,000	505,000
TDRs defaulted		$ 180,000		180,000
Net charge-offs			2,454,000	4,965,000
Commercial and Industrial [Member] | Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Annual sales of borrowers			100,000,000
Unfunded Loan Commitment [Member]
Financing Receivable, Recorded Investment [Line Items]
Modifications loans			$ 1,700,000	$ 1,000,000